UNNEST

Definition

The UNNEST function takes an ARRAY and returns a table with a row for each element in the ARRAY.

Syntax

UNNEST(ARRAY) [WITH OFFSET]

SELECT
  *
FROM
  UNNEST([1, 2, 2, 5, NULL]) AS unnest_column

The optional WITH OFFSET clause provides an additional column containing the position of each element in the array (starting at zero) for each row produced by UNNEST.

SELECT
  *
FROM
  UNNEST([1, 2, 2, 5, NULL]) AS unnest_column WITH OFFSET AS `offset`

Practical Info

Common Questions

How can I quickly generate a table of values in BigQuery?

You can use UNNEST to quickly create simple tables from arrays. For example:

SELECT
  *
FROM
  UNNEST(
       ARRAY<STRUCT<fruit STRING , number INT64>>[
         ('apples', 4), ('pears', 6), ('bananas', 2)
       ]
  )
AS simple_table;

How do I join each element in an array column to its corresponding row?

You can do this with a CROSS JOIN. A cross join will take every individual element of your unnested array and join it back to its parent row. This will create multiple rows for each element of your array but you can then filter it down.

WITH fruit_baskets as 
(
  SELECT
    * 
  FROM
    UNNEST(
      ARRAY<STRUCT<fruit ARRAY<STRING>,basket STRING>>[
        (['bananas', 'apples', 'oranges'], 'basket 1'),
        (['bananas', 'oranges'], 'basket 2'),
        (['bananas', 'apples'], 'basket 3')
      ]
    )
  AS fruit
)

SELECT * 
FROM fruit_baskets 
CROSS JOIN UNNEST(fruit) as fruit_unnest

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